There have been complaints about strange noises from a nearby tomb, so we must investigate what's wrong.
First, get to the tomb:

Once inside, we need to put the stones on the respective symbols to open the gates.

The mummy has forgot in which jar he put his liver while cleaning the place, so we have to get to the jars by opening the gates with levers, and find which jar has the liver and return it to the mummy

Once we help him find it, he shows us the path to the super secret area of the tomb.
Put the shaped stones in pits and put the red stones on the marks to open the gate and get the plate piece.

Talk to the priest of Isis to complete the quest.
The key to the gate is obtained as a quest reward.

Talk to Vladimir the mummy in town and a new quest begins.
Even though we've found the liver for the mummy, he can't go out like that, so the next quest is about finding a coat and a hat for him, which should be there in a part of the same tomb he was guarding, key to which we got as the quest reward.
Open the gate and then move the orange stones in place to open another gate before finally reaching the place where the hat and coat are stored.

Take the clothes and talk to Vladimir the mummy in town to complete the quest and get another plate piece as reward!
_________________________________________________________________________
Complete walkthrough video: https://youtu.be/nEQtJ4eSGkI